Quantifying the energy balance between the turbulent ionised gas and young stars

Abstract

Context. Stellar feedback is a key contributor to the morphology and dynamics of the interstellar medium in star-forming galaxies. In particular, energy and momentum input from massive stars can drive the turbulent motions in the gas, but the dominance and efficiency of this process are unclear. The study of ionised superbubbles enables quantitative constraints to be placed on the energetics of stellar feedback. Aims. We directly compare the kinetic energy of expanding superbubbles and the turbulent motions in the interstellar medium with the mechanical energy deposited by massive stars in the form of winds and supernovae. With such a comparison, we aim to determine whether the stellar feedback is responsible for the observed turbulent motions and to quantify the fraction of mechanical energy retained in the superbubbles. Methods. We investigated the ionised gas morphology, excitation properties, and kinematics in 19 nearby star-forming galaxies from the PHANGS-MUSE survey. Based on the distribution of the flux and velocity dispersion in the Hα line, we selected 1484 regions of locally elevated velocity dispersion (σ(Hα) > 45 km s−1), including at least 171 expanding superbubbles. We analysed these regions and related their properties to those of the young stellar associations and star clusters identified in PHANGS-HST data. Results. We find a good correlation between the kinetic energy of the ionised gas and the total mechanical energy input from supernovae and stellar winds from the stellar associations. At the same time, the contribution of mechanical energy injected by the supernovae alone is not sufficient to explain the measured kinetic energy of the ionised gas, which implies that pre-supernova feedback in the form of radiation and thermal pressure as well as winds is necessary. We find that the gas kinetic energy decreases with metallicity for our sample covering Z = 0.5 − 1.0 Z⊙, reflecting the lower impact of stellar feedback. For the sample of well-resolved superbubbles, we find that about 40% of the young stellar associations are preferentially located in their rims. We also find a slightly higher (by ∼15%) fraction of the youngest (< 3 Myr) stellar associations in the rims of the superbubbles than in the centres and the opposite trend for older associations, which implies possible propagation or triggering of star formation. Conclusions. Stellar feedback is the dominant source for powering the ionised gas in regions of locally (on a 50–500 pc scale) elevated velocity dispersion, with a typical coupling efficiency of 10 − 20%. Accounting for pre-supernovae feedback is required to set up the energy balance between gas and stars.

A Search for Correlations between Turbulence and Star Formation in THINGS Galaxies

“…The rate generally depends on the gas mass and density, with molecular cloud cores ultimately undergoing gravitational collapse (Jin et al 2017;Vázquez-Semadeni et al 2019;Rosen et al 2020). Additional stimuli come from some of the same processes that generate turbulence, like pressures from young stars (e.g., Egorov et al 2023), turbulent flow convergence and cloud collisions (e.g., Hartmann et al 2001;Suwannajak et al 2014;Wu et al 2018;Fukui et al 2021), and spiral shocks (Kim & Ostriker 2006;Elmegreen & Elmegreen 2019). There are also impediments to collapse such as ISM stabilization by rotation and turbulence (Martig et al 2008), cloud heating and disruption by young stars (e.g., Haid et al 2019;Chevance et al 2020;Lu et al 2020;Grudić et al 2022), and density restructuring by shear and cloud collisions in turbulent and galactic-scale flows (Federrath 2015;Hayward & Hopkins 2017, and references therein).…”

Hα Emission and H ii Regions at the Locations of Recent Supernovae in Nearby Galaxies

“…They found evidence for substantial populations of SNe away from CO emission and well-positioned to explode into low-density regions. Even SNe close to star-forming regions of galaxies can still go off in the low-density environments found in bubbles carved out by stellar populations and previous SNe (Bagetakos et al 2011;Pokhrel et al 2020;Barnes et al 2023;Egorov et al 2023;Watkins et al 2023aWatkins et al , 2023b.…”

Investigating the Drivers of Electron Temperature Variations in H ii Regions with Keck-KCWI and VLT-MUSE

“…As for ionized gas, Egorov et al (2023) identify in the PHANGS-MUSE galaxies more than 1400 regions of ionized gas with elevated intrinsic Hα velocity dispersions >45 km s −1 , and under the assumption that these regions are undergoing expansion, Egorov et al (2023) infer expansion velocities between v exp = 10-40 km s −1 (see also Egorov et al 2014Egorov et al , 2017Cosens et al 2022). The ubiquity of H II region expansion, as well as its effects on the surrounding molecular gas, makes it a good candidate to be a driver of low-velocity shocks capable of boosting [O III] temperatures.…”